Electrostatic air cleaners are widely used in air circulating systems, such as heating, ventilating, and air conditioning systems, to remove dust and other contaminants from the air circulating through the system. Electrostatic air cleaners employ a highly charged grid that applies an electrical charge to the dust and contaminants passing through it, and oppositely charged collectors to attract the charged dust and contaminant particles. While these systems are very beneficial and effective, they can be difficult to install, and more particularly difficult to retrofit in existing air circulating systems. This difficulty is at least in part due to the fact that if the electrostatic air cleaner operates when the air is not circulating in the air circulating system, the electrostatic air cleaner generates ozone. Thus the electrostatic air cleaner must generally be wired into air circulating system to prevent this undesirable result, and thus installation of electrostatic air cleaners is complicated and time-consuming, and often requires professionals. Previous attempts have been made to provide an electrostatic air cleaner that can sense air flow, see, for example Baysinger, U.S. Pat. No. 3,989,486, incorporated herein by reference. However, these systems generally relied upon diaphragm operated electromechanical or electronic switches or thermistors for measuring pressure differentials between the air circulating system and the ambient environment.
In modern high efficiency sealed systems, the pressure differential between the system and the ambient is unknown, and thus is it difficult to implement such a system. In installations in garages and attics natural convective currents may "fool" these prior systems into activating the electronic air cleaning system, even though the system blower is off.
One attempt to overcome these difficulties is the use of a sail switch, which detects air flow within the system, but these switches are typically very large and thus cannot be incorporated into a self-contained electrostatic air cleaning system, and must be mounted remotely.
Moreover, it is difficult to mount conventional electrostatic air cleaners in the small enclosures provided in some new construction. Some electrostatic cleaners have cover mounts that require clearance around the covers which prevent mounting the cleaners in tight spaces. Other electrostatic air cleaners have covers with components that protrude beyond the profile of the frame opening, also preventing the cleaner from being mounted in tight spaces. This problem was exacerbated by the fact that in conventional electrostatic air cleaners, the cover could typically only be mounted in one orientation, limiting how the electrostatic air cleaner could be incorporated into the air circulating system.